Don't set top and bottom anchors since verticalCenter is used
AbstractApplicationHeader sets verticalCenter on its children, so remove the explicit top/bottom anchors.
Was causing this error at runtime:
/usr/lib64/qml/org/kde/kirigami/private/globaltoolbar/PageRowGlobalToolBarUI.qml:55:5: QML Rectangle: Cannot specify top, bottom, and verticalCenter anchors at the same time.
Pinging @mart @jblackquill since it's your code that's colliding